In the 1800s, Americans planted tamarisk for windbreaks and erosion control; by 2005, the tree had spread across western river systems and become a major management concern

In the late 19th century, tamarisk was introduced to the United States for practical purposes, including use as windbreaks and erosion-control plantings. Over time, the tree spread along waterways across the American West. In testimony before the U.S. House Subcommittee on Forests and Forest Health on July 14, 2005, Department of the Interior Science Advisor Dr James Tate reported estimates that tamarisk covered between 500,000 and 1.5 million acres of riparian land across all 17 western states. The testimony on H.R. 2720, the Salt Cedar and Russian Olive Control Demonstration Act, described why the spread of the plant had become a management concern, particularly in relation to water, native vegetation and wildlife.

How tamarisk became a western water concern

Tamarisk was well suited to many western river environments. The Department of the Interior's 2005 testimony said the plant could spread rapidly into newly exposed areas following floods, while its dense growth and ability to deposit salt into soil could make established stands difficult to manage. The testimony also reported that studies had found the densest tamarisk stands could use slightly more water each day than native cottonwood-willow plant communities. Where the trees grew in streambeds, they could slow water movement and allow more water to percolate into surrounding sediments. The Department presented these characteristics as factors that could affect water availability in some western river systems, particularly where dense vegetation occupied channels through which reservoir water was released for irrigation.


The testimony also cited economic estimates associated with water losses. It reported that the estimated value of losses involving irrigation and municipal uses, flood control and hydropower ranged from $133 million to $265 million, while irrigation losses alone were estimated at up to $120 million a year. The Department cited Patricia Zavaleta's Valuing Ecosystem Services Lost to Tamarix Invasion in the United States among the sources behind these estimates. The figures represented estimates of the economic value associated with water losses and related services, so they should not be read as a direct calculation of the amount of water consumed by tamarisk.

The Department's concern therefore extended beyond the tree's individual water use. Its testimony described control efforts that also sought to improve stream flow where appropriate, restore native vegetation along riverbanks and floodplains, reduce hazardous fuels and improve wildlife habitat. Because tamarisk occurred across different ownerships and jurisdictions, management involved federal agencies, states, tribes, local governments, researchers, private landowners and conservation groups.

The Department highlighted the 2004 Team Tamarisk: Cooperating for Results conference in Albuquerque, where 300 representatives from federal, state, local and tribal organisations and the private sector discussed tamarisk control and the development of sustainable habitats. The National Invasive Species Council also established a team of economists, ecologists, biologists and engineers from the public and private sectors to analyse alternative tamarisk management strategies in the Rio Grande-Pecos and Colorado River basins.

Technology formed another part of the response. Scientists from the U.S. Geological Survey, NASA's Goddard Space Flight Center and Colorado State University used ground samples and MODIS satellite data to model areas suitable for tamarisk. The Department said this work could help managers understand the plant's existing and potential distribution and support early detection and rapid response. Separately, the USGS National Institute of Invasive Species Science was compiling records from more than 50 groups, with just under 35,000 locations being assembled into a central database and map.

Why removing tamarisk was only part of the solution

The Department's testimony described the use of mechanical, chemical and physical methods to clear tamarisk from areas containing important wildlife resources. But removal was only one element of the work. Managers also had to consider how native vegetation could be restored and how reinfestation could be limited, particularly where tamarisk occurred in areas used by sensitive wildlife.

Bosque del Apache National Wildlife Refuge in New Mexico was one location where different approaches were being tested at the time of the testimony. The Department described experiments involving biomass removal, intermittent flooding, chemical treatments and mechanical methods, alongside work to restore native riparian vegetation and reduce reinfestation. The project also involved nearby landowners and tribes.

Water management formed another part of the research. On Arizona's Bill Williams River, resource managers had used a managed streamflow release intended to encourage native riparian plants while inhibiting tamarisk regeneration. Elsewhere, researchers from the USGS, University of Denver, and Bureau of Reclamation were examining the salinity and drought tolerance of native Rio Grande plants to identify species suitable for revegetation. Other experiments examined whether mycorrhizal fungi could influence the establishment and growth of native plants.

Biological control was also under investigation. Federal agencies and university researchers were testing potential control agents, including beetles, alongside other research into tamarisk management. The Department noted that the endangered southwestern willow flycatcher occupied some areas then infested with tamarisk, where native willows and cottonwoods had previously grown. This overlap meant that control methods had to be evaluated alongside their potential effects on wildlife habitat. (

Management also extended beyond federal land. The Fish and Wildlife Service's Partners for Fish and Wildlife programme provided technical and financial assistance for habitat restoration on private land, while the DOI testimony identified tamarisk control as one focus of such assistance in the Southwest. The Department also described involvement by local governments, tribes, volunteers and conservation organisations, reflecting the need for cooperation where restoration crossed different properties.

H.R. 2720 proposed a more systematic assessment of the problem. Under the Salt Cedar and Russian Olive Control Demonstration Act, Congress directed the Department of the Interior to assess the extent of salt cedar and Russian olive infestations, review existing control research, consider the feasibility of reducing water consumption, examine restoration challenges, and estimate the costs of removal, biomass disposal, restoration, and maintenance. The Department supported the broader idea of a comprehensive assessment but raised concerns about some of the bill's funding and mandatory provisions.

The history of tamarisk in the American West shows how a plant introduced for practical purposes eventually required a more complex management response. By the time of the Department of the Interior's July 2005 testimony, the response described in the document included mapping, early detection, control, restoration research, and partnerships aimed at protecting water resources and wildlife habitat. Rather than presenting removal as the only objective, the testimony described efforts to control tamarisk while encouraging the recovery of native vegetation across affected western river systems.